The objectives of this project are to clone the vermilion locus of Drosophila, to study the structure and expression of the gene, and to investigate the nature of vermilion mutations that can be suppressed by mutating the suppressor of sable locus. Vermilion encodes the enzyme tryptophan oxygenase which catalyzes the first step in the synthesis of the brown eye pigment. DNA from this locus was cloned from a mutant containing a P element insertion at vermilion by "transposon tagging." The cloned DNA hybridizes to the polytene chromosome band that contains vermilion. Furthermore, DNAs from a number of vermilion mutants shown detectable aberrations in the region homologous to the cloned DNA. Severl spontaneous mutations at vermilion, sable, purple, and speck are suppressible by mutations at suppressor of sable. Using cloned vermilion DNA probes, we have determined that these supressible vermilion alleles are DNA insertion mutations, and DNAs from several of these mutants have been cloned. The mutants v1, v2, and vk are insertions of the copia-like element known as 412. The weakly suppressible mutant v36i contains an insertion of the element known as roo or B104. The vermilion transcript, 1.4 kb long, originates from the same DNA region where the mutations occur. Transposable element insertion mutations disrupt the production of this transcript. Work is continuing to determine how this disruption occurs and how suppressor of sable restores function to the locus.